The present invention relates to the field of audio-visual signal transmission and reception. More particularly, the present invention relates to a method and apparatus for scrambling an audio-visual signal during transmission in order to control reception and use of the signal.
Cable and pay-per-view television programming are extremely popular and widely available in modern society. Those firms providing such programming are frequently lucrative and successful. This success comes from the ability to prevent those who have not purchased the service from receiving and using the audio-visual signals transmitted by the service provider.
In general, it is common for a cable company or other service provider to scramble its signals to prevent their use by unauthorized parties. This scrambling is intended to make the signals unintelligible to typical television sets which are not authorized to receive and use the scrambled signal. When the signal is scrambled, a conventional television will not recognize the signal, or at best, display a distorted image from the signal.
Cable companies which provide a number of channels over a cable connection may only scramble certain channels so that cable subscribers can be required to pay additional fees for receiving these xe2x80x9cpremiumxe2x80x9d channels. The premium channels are typically movie or adult channels.
Those subscribers who have paid the service provider for reception of the scrambled signal will be given equipment for use with their television sets which unscrambles the signal. With this equipment, the authorized user can unscramble and receive the service provider""s signals and view the programming contained in the transmission.
A well-known conventional method of scrambling a signal to prevent its unauthorized reception is to reverse the spectral positions of the audio and video portions of the signal. Typically, an audio-visual signal will have an audio carrier signal at a first frequency and a video carrier signal at a second frequency. The carrier signals are modulated to carry the respective video and audio data of the transmitted programming.
If, however, the audio carrier signal is transmitted at the second (video carrier) frequency, and the video carrier signal is transmitted at the first (audio carrier) frequency, the signal is scrambled. A television tuner will be attempting to receive the audio signal at the first frequency and the video signal at the second frequency, and will be unable to receive the reversed signal properly.
This method of scrambling an audio-visual signal is not wholly satisfactory, however, for the following reasons. The 4.5 Mhz audio beat may still be received by the unauthorized television. Then, if the television set is fine tuned, it may be possible to receive the picture portion of the signal. The picture will most likely be stripped of its color information and appear in black and white, but the unauthorized user may in this way obtain limited use of the scrambled signal. If the picture signal contains adult programming, even this limited visibility may be a problem under federal regulation.
Accordingly, there is a need in the art for a low-cost, but more effective means and method of scrambling an audio-visual signal.
It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a method and device for scrambling an audio-visual signal and for receiving the scrambled signal that is both effective and inexpensive.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied as an audio-visual signal reception system for receiving both scrambled and unscrambled signals which includes: a tuner for receiving an incoming signal that may or may not be scrambled; a dual-side local oscillator providing an oscillations signal in response to whether the incoming signal is scrambled or unscrambled; and a mixer for receiving the incoming signal and the oscillation signal and outputting an intermediate frequency signal.
If the incoming signal is scrambled, the dual-side oscillator functions as a low-side oscillator and provides the oscillation signal at a frequency lower than a frequency of the incoming signal. The mixer then subtracts the oscillation signal from the incoming signal to produce the intermediate frequency signal.
If the incoming signal is unscrambled, the dual-side oscillator functions as a high-side oscillator and provides the oscillation signal at a frequency higher than a frequency of the incoming signal. The mixer then subtracts the incoming signal from the oscillation signal to produce the intermediate frequency signal.
The voltage supplied to the dual-side local oscillator is provided and regulated by an independent voltage controller. The voltage input to the oscillator is determined in response to whether the incoming signal is scrambled or unscrambled.
After the intermediate frequency signal is produced, an intermediate frequency signal to baseband signal processor converts the intermediate frequency signal to a baseband signal. The baseband signal can then be displayed by the television set.
The present invention also encompasses a method of receiving scrambled audio-visual signals. The method includes the steps of: receiving an incoming signal (which may be scrambled or unscrambled) with a tuner; providing an oscillation signal with a dual-side local oscillator in response to whether the incoming signal is scrambled or unscrambled; and mixing the incoming signal and the oscillation signal with a mixer and outputting a resulting intermediate frequency signal.
If the incoming signal is scrambled, the method proceeds by (1) providing, with the dual-side oscillator, the oscillation signal at a frequency lower than the frequency of the incoming signal, and (2) subtracting, with the mixer, the oscillation signal from the incoming signal to produce the intermediate frequency signal.
If the incoming signal is unscrambled, the method proceeds by (1) providing, with the dual-side oscillator, the oscillation signal at a frequency higher than the frequency of the incoming signal, and (2) subtracting, with the mixer, the incoming signal from the oscillation signal to produce the intermediate frequency signal.
Preferably, the method of the present invention also includes independently controlling the voltage input to the dual-side oscillator with an independent voltage controller in response to whether the incoming signal is scrambled or unscrambled. Finally, the method may include converting the intermediate frequency signal to a baseband signal.